This invention relates to apparatus for forming pads of material from a more compressed form of the same material, and in particular to apparatus for forming the pads in the shape and contour required, including varying the thickness across the width and length of the pads, without the need for later cutting and trimming and the resultant waste.
The conventional method for forming fibrous pads begins by feeding a felted web of compressed material such as wood pulp into a hammermill, where it is defibrated to a light, fluffy material called "fluff". This fluff is then drawn through the screen of the hammermill and onto a screen belt by a source of vacuum below the belt. There is thus formed on the belt a fluff blanket of relatively uniform thickness of about one inch, more or less, across the entire width of the belt, which can be up to 24 inches or more. This blanket of fluff is then conveyed continuously downstream to machines which process it into the particular end products being manufactured, whether they be feminine hygiene pads, disposable diapers, adult incontinence products or other products employing fluff pads.
Conventionally, the processing includes cutting the blanket into the proper shape for the particular product being manufactured, and then wrapping and packaging it for later use. Cutting the blanket into the proper shape, however, can result in a substantial waste of fluff. For instance, to form a product such as a feminine hygiene pad, the blanket must be cut into oval shapes. Generally this is done by use of a rotary die cutter. This creates a "dog-bone" shaped waste between the ends of the respective ovals.
If on the other hand the product is a disposable diaper or adult incontinence product, no waste is created by the cut between the pads, since the edges are straight. The sides, however, are usually cut in the shape of an hourglass to allow space for the legs of the wearer without causing bunching. The cuts required to allow space for the legs again cause waste of fluff.
Moreover, the mere fact that the fluff blanket must be cut at all is a substantial disadvantage. As to the rotary die cutter mentioned above, the tolerances for cutting fluff are extremely close, and so the maintenance costs can be very high. Additionally, any fluff that is cut using a rotary die cutter is left with a very hard edge, since the fluff is very tightly compressed at the edge by such a cutter at the time of cutting. Because such a hard edge would be objectionable for the leg cutouts of disposable diapers and adult incontinence products, due to the skin irritation such a hard edge would cause, water-jet cutting has come to be the conventional method of forming the "hourglass" cuts required, because it results in a fluffy, soft cut edge. Of course water-jet cutting has its own disadvantage, that is, extremely high maintenance costs. These high costs arise from the fact that the water must be forced at extremely high pressure through a fine nozzle:, causing the nozzle to experience high wear rates almost regardless of the material from which the nozzle is made. Further, for the water to be reused in a continuous cutting operation, it must be carefully filtered to avoid clogging the nozzle.
A further disadvantage of the above-described system lies in the screen belt on which the fluff blanket is formed. This screen belt is tautly stretched over the rollers on which it runs. The fact that the screen itself runs on the rollers and is pulled across a vacuum box, which has a perforated top cover, produces friction which causes wear to the screen. As the screen wears, fine bits of metal wire may wear off and may become entangled in the fluff blanket. This situation may give the unsatisfactory result that diapers and feminine hygiene pads may have bits of metal in them, which would cause great irritation or worse.
The entire process of forming a uniform fluff blanket and then cutting fluff pads therefrom has at least one other significant disadvantage: the uniformity of the blanket itself. Thus for instance the absorbent padding of a disposable diaper is the same thickness at the waist portion, which seldom gets wet, as it is between the legs where much moisture must be absorbed, because the thickness of the blanket from which it was cut was uniform throughout its length and width.
Finally, referring to the waste of fluff alluded to above, the raw material used to make this fluff, such as wood pulp, is expensive. Costly machines have been designed and sold simply to recycle, reprocess and reuse this fluff cut out of the shapes described above to avoid discarding this waste and the cost associated therewith.
A patent to Furbeck, U.S. Pat. No. 3,717,905 discloses an apparatus for forming fibrous pads, although that apparatus employs a seal roll as a required component. Two other patents, one to Savich, U.S. Pat. No. 3,939,240 and one to Kolbach, U.S. Pat. No. 3,973,291, disclose methods for forming fibrous pads. Kolbach's method includes a screened belt, which slides over multiple vacuum boxes, with all of the wear problems attendant thereto. Savich's method includes forming larger pads and passing them through smaller openings as a means of forming and compressing the pads. Applicant has discovered that the pads, once formed, do not hold their shape well if later compressed or forced through smaller openings.
This invention relates to solutions to the problems described herein.